3,5,6-Trichloropyridin-2-ol is an intermediate in the manufacture of several agricultural pesticides, e.g., chlorpyrifos, chlorpyrifos-methyl and triclopyr. U.S. Pat. No. 4,327,216 describes a process for preparing a mixture of 2,3,5,6-tetrachloropyridine and 3,5,6-trichloropyridin-2-ol by reacting trichloroacetyl chloride with acrylonitrile in the presence of a catalyst.
The following series of reactions is responsible for the products obtained in said patent (Scheme I). ##STR1## Although the series of reactions is advantageously carried out in a single operation and in a closed system under pressure, the combined yield of 2,3,5,6-tetrachloropyridine and 3,5,6-trichloropyridin-2-ol is not very high. Furthermore, the reaction typically produces a mixture of the two products which must be separated or treated in subsequent operations to convert one product into the other. It is desirable to have a process to prepare 3,5,6-trichloropyridin-2-ol in higher yields and without any tetrachloropyridine by-product.